Bookmark button: the "star" button that is used
to bookmark pages. Extensions may remove this button using the settings
overrides, and optionally replace it with a browser action or page action.

Bookmark shortcut: the shortcut key that is used
to bookmark a page (Ctrl-D on Windows). Extensions may remove this shortcut
via the settings overrides, and optionally bind their own command to it
using the commands section of the manifest. If the shortcut key
is removed or rebound, the corresponding menu item as also removed or
overridden respectively.

Note: Settings overrides for bookmarks_ui are only enabled
in the Chrome Dev release, and Chrome must be started with the
--enable-override-bookmarks-ui=1 command line flag to enable
bookmarks user interface overrides.

Reference

An extension can override one or more of the following properties in the
manifest: